A method of synthesizing bis-(1(2)H-tetrazol-5-yl)-amine is described by William P. Norris and Ronald A. Henry, "Cyanoguanyl Azide Chemistry," Journal of the American Chemical Society, pp. 650-660, March 1964, which is incorporated herein by reference. Bis-(1(2)H-tetrazol-5-yl)-amine (herein after referred to as BTA) has the following structure: ##STR1## The BTA synthesis method described by Norris et al. reacts sodium dicyanamide (0.1 mole), sodium azide (0.22 mole), and trimethylammonium chloride catalyst (0.22 mole) in 100 ml of water at refluxing temperature for 23 hours.
The Norris et al. process has several significant disadvantages. For instance, the tertiary alkyl amine catalyst used by Norris et al., trimethylammonium hydrochloride, is not available on a large scale and is expensive. Furthermore, the tertiary alkyl amine is released during the reaction process, and it has a pungent, obnoxious odor. It will be appreciated that it would be an advancement in the art to provide a process of preparing BTA which uses a readily available, low cost catalyst which does not smell bad.
Another important disadvantage of the Norris et al. process is the use of excess sodium azide. Because excess sodium azide is used, sodium azide is present throughout the reaction process and is left over upon completion. This represents a safety and disposal concern. In addition, according to the reaction process of Norris et al., treatment of the final reaction mixture with acid results in the formation of hydrazoic acid (HN.sub.3) which is a vasodilator and explosive. It would be a significant advancement in the art to provide a process of preparing BTA which avoids or minimizes the formation of hydrazoic acid.
Yet another disadvantage of the Norris et al. process is in purification of the final product. Norris et al. teaches that the hot reaction mixture is treated with concentrated hydrochloric acid and then cooled. This results in entrapment of the sodium salt within the particles. Since an important use of the final BTA product is as the primary fuel of a gas generant composition, particle purity is important. It is known that contaminants, including salts such as chloride and sodium salts, adversely affect burn rate. Accordingly, it would be an advancement in the art to provide a process of preparing BTA having a purity suitable for use in gas generant devices.
The Norris et al. process consistently produces large crystals. It has been found that this results from final acidification at high temperature. Small, rounded particles having a high surface area are often preferred in gas generant formulations. Thus, it would be an advancement in the art to provide a process of preparing BTA which produces small, rounded BTA particles.
Such processes for preparing BTA are disclosed and claimed herein.